In manufacturing advanced devices, it may be necessary to process a substrate having a non-planar surface. Examples of such devices include three dimensional (3D) FinFETs having raised fins with horizontally and vertically oriented surface sections, and CMOS image sensors (CIS) and eDRAMs each of which has trenches with horizontally and vertically oriented surface sections. One of the techniques used to process such a substrate may include doping to modify electrical, mechanical, optical, and thermal properties, or a combination of such properties, of the original substrate. The source/drain (SD) regions of FinFETs, sidewall of shallow trenches in CMOS image sensors, and sidewall of deep trenches (DT) in eDRAMs may be doped to modify the properties of the substrates.
The doping technique may be performed via an ion implantation, a particle based step. In an ion implantation, ions are generated in an ion source. Thereafter, ions are directed toward a substrate located downstream of the ion source at a single, uniform or substantially uniform angle. The ions are then incident on the substrate surface and process the substrate.
The ion implantation techniques, whether for planar or non-planar substrate, are line-of-sight techniques. The surface sections perpendicular or substantially perpendicular to the incident angle of the ions are sufficiently exposed and processed effectively. Other surface sections oriented at another angle, however, may not be exposed as sufficiently, and the surface may not be processed as effectively. In a plasma based doping technique, for example, a region of the substrate near the surface sections perpendicular or substantially perpendicular to the ion flux may be doped at much higher dose (e.g. up to 10 to 100 times) than other regions near the surface sections parallel to the ion flux. As a result, a non-conformal processing may occur. Such a variation in processing may result in substrates with non-uniform properties, and the final devices may not operate optimally.
As the advanced devices require uniform properties, it may be desirable for the techniques to conformally process surfaces oriented in different angles. In the doping techniques, for example, it may be desirable to achieve equal or substantially equal dopant concentration in the regions near the differently oriented surface sections. Although numerous techniques have been proposed, the proposed techniques achieved limited success. Accordingly, a new technique is needed.